Before the present invention, aspirating and/or irrigating apparatus were known, and tended to be used to remove wound exudate during wound therapy. In known forms of such wound therapy, the offtake from the wound, especially when in a highly exuding state, is voided to waste, e.g. to a collection bag.
Materials deleterious to wound healing are removed in this way. However, materials that are beneficial in promoting wound healing, such as growth factors, cell matrix components, and other physiologically active components of the exudate from a wound are lost to the site where they can be potentially of most benefit, i.e. the wound bed, when such therapy is applied.
Such known forms of wound dressing and aspiration and/or irrigation therapy systems thus often create a wound environment under the dressing that may result in the loss of optimum performance of the body's own tissue healing processes and in slow healing, and/or in weak new tissue growth that does not have a strong three-dimensional structure adhering well to and growing from the wound bed. This is a significant disadvantage, in particular in chronic wounds.
It thus would be desirable to provide a system of therapy which    a) can remove materials deleterious to wound healing from wound exudate, whilst    a) retaining materials that are beneficial in promoting wound healing in contact with the wound bed.
Dialysis is a known method of treating bodily fluids such as blood ex vivo, to cleanse them of materials that are deleterious to the body systemically. Removal of such materials by contact with the dialysate is the prime purpose of dialysis, whilst also retaining materials such as blood, cells and proteins. Other materials that may have an additional positive therapeutic action are potentially lost to the system through the dialysis membrane, which is also permeable to them. The balance of such materials in the bodily fluid in recirculation may thus be further depleted.